[tip: x86/bugs] x86/bugs: Add AUTO mitigations for mds/taa/mmio/rfds

tip-bot2 for David Kaplan
2025-02-28T11:53:45Z

The following commit has been merged into the x86/bugs branch of tip:

Commit-ID: b8ce25df2999ac6a135ce1bd14b7243030a1338a
Gitweb: https://git.kernel.org/tip/b8ce25df2999ac6a135ce1bd14b7243030a1338a
Author: David Kaplan <david.kaplan@amd.com>
AuthorDate: Wed, 08 Jan 2025 14:24:43 -06:00
Committer: Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Fri, 28 Feb 2025 12:40:21 +01:00

x86/bugs: Add AUTO mitigations for mds/taa/mmio/rfds

Add AUTO mitigations for mds/taa/mmio/rfds to create consistent vulnerability
handling. These AUTO mitigations will be turned into the appropriate default
mitigations in the <vuln>_select_mitigation() functions. Later, these will be
used with the new attack vector controls to help select appropriate
mitigations.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20250108202515.385902-4-david.kaplan@amd.com
---
arch/x86/include/asm/processor.h | 1 +
arch/x86/kernel/cpu/bugs.c | 20 ++++++++++++++++----
2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index c0cd101..90278d0 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -757,6 +757,7 @@ extern enum l1tf_mitigations l1tf_mitigation;

enum mds_mitigations {
MDS_MITIGATION_OFF,
+ MDS_MITIGATION_AUTO,
MDS_MITIGATION_FULL,
MDS_MITIGATION_VMWERV,
};
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 4269ed1..93c437f 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -238,7 +238,7 @@ static void x86_amd_ssb_disable(void)

/* Default mitigation for MDS-affected CPUs */
static enum mds_mitigations mds_mitigation __ro_after_init =
- IS_ENABLED(CONFIG_MITIGATION_MDS) ? MDS_MITIGATION_FULL : MDS_MITIGATION_OFF;
+ IS_ENABLED(CONFIG_MITIGATION_MDS) ? MDS_MITIGATION_AUTO : MDS_MITIGATION_OFF;
static bool mds_nosmt __ro_after_init = false;

static const char * const mds_strings[] = {
@@ -249,6 +249,7 @@ static const char * const mds_strings[] = {

enum taa_mitigations {
TAA_MITIGATION_OFF,
+ TAA_MITIGATION_AUTO,
TAA_MITIGATION_UCODE_NEEDED,
TAA_MITIGATION_VERW,
TAA_MITIGATION_TSX_DISABLED,
@@ -256,27 +257,29 @@ enum taa_mitigations {

/* Default mitigation for TAA-affected CPUs */
static enum taa_mitigations taa_mitigation __ro_after_init =
- IS_ENABLED(CONFIG_MITIGATION_TAA) ? TAA_MITIGATION_VERW : TAA_MITIGATION_OFF;
+ IS_ENABLED(CONFIG_MITIGATION_TAA) ? TAA_MITIGATION_AUTO : TAA_MITIGATION_OFF;

enum mmio_mitigations {
MMIO_MITIGATION_OFF,
+ MMIO_MITIGATION_AUTO,
MMIO_MITIGATION_UCODE_NEEDED,
MMIO_MITIGATION_VERW,
};

/* Default mitigation for Processor MMIO Stale Data vulnerabilities */
static enum mmio_mitigations mmio_mitigation __ro_after_init =
- IS_ENABLED(CONFIG_MITIGATION_MMIO_STALE_DATA) ? MMIO_MITIGATION_VERW : MMIO_MITIGATION_OFF;
+ IS_ENABLED(CONFIG_MITIGATION_MMIO_STALE_DATA) ? MMIO_MITIGATION_AUTO : MMIO_MITIGATION_OFF;

enum rfds_mitigations {
RFDS_MITIGATION_OFF,
+ RFDS_MITIGATION_AUTO,
RFDS_MITIGATION_VERW,
RFDS_MITIGATION_UCODE_NEEDED,
};

/* Default mitigation for Register File Data Sampling */
static enum rfds_mitigations rfds_mitigation __ro_after_init =
- IS_ENABLED(CONFIG_MITIGATION_RFDS) ? RFDS_MITIGATION_VERW : RFDS_MITIGATION_OFF;
+ IS_ENABLED(CONFIG_MITIGATION_RFDS) ? RFDS_MITIGATION_AUTO : RFDS_MITIGATION_OFF;

static void __init mds_select_mitigation(void)
{
@@ -285,6 +288,9 @@ static void __init mds_select_mitigation(void)
return;
}

+ if (mds_mitigation == MDS_MITIGATION_AUTO)
+ mds_mitigation = MDS_MITIGATION_FULL;
+
if (mds_mitigation == MDS_MITIGATION_FULL) {
if (!boot_cpu_has(X86_FEATURE_MD_CLEAR))
mds_mitigation = MDS_MITIGATION_VMWERV;
@@ -514,6 +520,9 @@ static void __init rfds_select_mitigation(void)
if (rfds_mitigation == RFDS_MITIGATION_OFF)
return;

+ if (rfds_mitigation == RFDS_MITIGATION_AUTO)
+ rfds_mitigation = RFDS_MITIGATION_VERW;
+
if (x86_arch_cap_msr & ARCH_CAP_RFDS_CLEAR)
setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
else
@@ -1979,6 +1988,7 @@ void cpu_bugs_smt_update(void)

switch (mds_mitigation) {
case MDS_MITIGATION_FULL:
+ case MDS_MITIGATION_AUTO:
case MDS_MITIGATION_VMWERV:
if (sched_smt_active() && !boot_cpu_has(X86_BUG_MSBDS_ONLY))
pr_warn_once(MDS_MSG_SMT);
@@ -1990,6 +2000,7 @@ void cpu_bugs_smt_update(void)

switch (taa_mitigation) {
case TAA_MITIGATION_VERW:
+ case TAA_MITIGATION_AUTO:
case TAA_MITIGATION_UCODE_NEEDED:
if (sched_smt_active())
pr_warn_once(TAA_MSG_SMT);
@@ -2001,6 +2012,7 @@ void cpu_bugs_smt_update(void)

switch (mmio_mitigation) {
case MMIO_MITIGATION_VERW:
+ case MMIO_MITIGATION_AUTO:
case MMIO_MITIGATION_UCODE_NEEDED:
if (sched_smt_active())
pr_warn_once(MMIO_MSG_SMT);